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post #1 of 3 (permalink) Old 02-03-13, 03:36 PM Thread Starter
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Idler Arm Bolts - Tap size???

All,

I have a 2003 F-150 with a 4.2L V6. I noticed during my last oil change that the idler arm grease boot was cracked, so I recently purchased a new one.

The 2 bolts that hold the idler arm to the frame came out just fine. But when it came time to attaching the new idler arm, I found it IMPOSSIBLE to screw the upper bolt in all of the way.

I figured that I needed to use a tap to clean up the existing tapped hole. So I measured the OD of the bolt with a digital caliper to be .625" OD. I have a thread pitch gage and measured the thread pitch to be 13 threads per inch.

I went to Autozone, and the only close thing that they had to .625-13 was the tap in a Fix-a-thread kit for .500-13 threaded inserts. The tap itself is about .607-13 (used for .500-13 "helicoils"), so I figured that this would be sufficient. There is no such thing as a .625-13 tap on Mcmaster Carr, MSC, Northern Tool, etc. So I cleaned out the thread with the .607-13 tap. The tap encountered some resistance in the same area that I encountered resistance, and it appeared to do a great job cleaning out the hole.

So I tried to screw the bolt back into the upper hole and I found that it is still IMPOSSIBLE to screw the bolt in all of the way. I have about 3/8" left before the bolt head bottoms out on the idler arm. I can see the opposite end of the hole from the right wheel well. I shot some lubricant in there...still no success.

So does anybody know the tap size for this hole???? Is it metric? When I converted .625-13 to metric, I did not see to find any decent matches.

Thanks in advance.
--Neal

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post #2 of 3 (permalink) Old 02-03-13, 04:18 PM Thread Starter
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Re: Idler Arm Bolts - Tap size???

All,

After re-assessing the situation, maybe a M16X2 tap would work. A M16 thread is only about .005" larger than a .625 thread.

And a thread pitch of 13 comes out to about .077" per thread or 1.95mm. Pretty close to 2mm.

--Neal
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post #3 of 3 (permalink) Old 02-03-13, 04:23 PM
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Re: Idler Arm Bolts - Tap size???

I'd take the good one out and see if you can match it up. Did you check to make sure the holes are the same distance apart as the old arm?

Bert
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